Many other signs therefore, Jesus also performed in the presence
of His disciples, which are not written in this book; but these have been
written that you may believe that Jesus is the Christ, the Son of God; and that
believing you may have life in His name. John 20:30,31

This is the plan of the Gospel of John. The author authenticates
his purpose by his conclusion: " This is the disciple who bears witness to these
things, and wrote these things; and we know that his witness is true. And there
are also many other things which Jesus did, which if they were written in
detail, I suppose that even the world itself would not contain the books which
were written. John 21:24,25